This invention relates to an external combustion engine of the kind comprising pressure vessel means defining a tubular working chamber having spaced apart first and second ends and including first wall means adjacent said first end of the chamber and second wall means adjacent said second end of the chamber, heating means for heating said first wall means, cooling means for cooling said second wall means, piston means having heat exchanging means and drive means for reciprocating the piston means within the tubular working chamber between said first and second ends of the chamber so that the working fluid passes through said heat exchanging means.
Most Stirling engines operate on the principle of expansion and contraction of a contained gaseous working fluid moving between two different temperature levels. Although Stirling engines have certain advantages compared with other heat engines, they face problems regarding sealing of the working fluid, e.g. hot hydrogen, and power control. In the 1920s, Malone proposed in U.S. Pat. No. 1,487,664 and U.S. Pat. No. 1,717,161 modifications to the basic design of Stirling engine which used, instead of gas as the working fluid, water which varied in condition between liquid and super-critical. The Malone engines needed to operate at high pressures and consequently provided high power densities. However, since the work by Malone, very little work has been undertaken to further develop the Malone engine. The only significant development in the Malone cycle has been in refrigeration and heat pumps.
The basic configuration of a known Malone engine comprises a thermodynamic pressure vessel (or xe2x80x9cTD pilexe2x80x9d) in the form of a long tube with opposite extremes of temperature applied to its opposite ends. The hot end is exposed to a heat source, such as a flame or heat storage material, whilst the cold end has a cooling jacket able to remove heat from the pile and transfer it to the cooling fluid, which is circulated through the jacket. Between these extremes of position and temperature inside the TD pile, is a porous piston which.is both a regenerator and displacer (hereinafter referred to as a regenerator). The regenerator is mechanically driven from end to end within the pile following a sinusoidal motion. As the regenerator is moved, fluid is forced through its core matrix, in the process exchanging heat between the matrix and the fluid. The displacement of fluid away from each end alternately reduces the mass of fluid available to either accept or give up heat.
Due to the forced motion of the regenerator and the cyclically varying ingress and egress of heat, there is a variation of pressure and volume of the fluid within the TD pile which can be harnessed to create mechanical work. It is also known to connect a piston to the cold end, which can allow the working volume to expand whilst at high pressure and then contract at reduced pressure, thereby forming an interface between fluid and mechanical power. More specifically, it has been proposed to provide a digital-displacement hydraulic pump/motor of the kind disclosed in EP-A-0494236 for controlling the working volume of the TD pile.
The present invention seeks to provide improvements in the basic components of an external combustion engine of the kind referred to.
According to one aspect of the present invention an external combustion engine of the kind referred to is characterised in that said first wall means has first heat exchange surface means and in that said piston means has valving means including first valve means positionable for directing the working fluid, after passage through said heat exchanging means, to flow over said first heat exchange surface means when the piston means is moving towards said second end of the chamber in order to move the working fluid from the second end to the first end of said chamber and to by-pass said first heat exchange surface means when the piston means is moving towards said first end of the chamber in order to move the working fluid from the first end to the second end of said chamber.
According to another aspect of the present invention there is provided an external combustion engine as claimed in the ensuing claim 20.
According to further aspect of the present invention there is provided an external combustion engine as claimed in the ensuing claim 23.
According to a still further aspect of the present invention there is provided an external combustion engine as claimed in the ensuing claim 24.